Self-cleaning Glaucoma Implant Could Improve Eye Treatment

Glaucoma is essentially a plumbing problem. The condition can happen when protective fluid builds up in the eye, putting pressure on the optic nerve and damaging a patient’s vision. One solution is surgically implanting devices — tiny drainage pipes and reservoirs — to release the pressure. But the narrow openings that make these implants unobtrusive also make them vulnerable to blockage.

A Purdue University research team recently published a proof-of-concept improvement for glaucoma implants. By outfitting a drainage tube with microscale components along its interior walls, the biomedical engineers created an implant that can clean itself.

“We're actively turning the devices on to essentially shake and vibrate,” said Hyowon Hugh Lee, the biomedical engineering professor who led the work.

The devices Lee and his students have designed are micron-sized magnetic cantilevers. In the presence of a switching magnetic field, the cantilevers bounce up and down, like the beating tail of a bacteria’s cilia. The bouncing microbeams the fluid within the tube, shaking material from the tube’s walls.

In experiments where Lee and his students coated drainage tubes with fluorescent-tagged proteins, microscopy showed that five minutes of these vibrations removed about 85 percent of the protein coating.

In the clinic, doctors have also explored using laser ablation or specialized enzymes to clear clogged glaucoma drainage devices. These approaches are fairly involved and pose some risks for patients. Lee designed his device to be less invasive, using custom-built electromagnets to externally activate cleaning.

Before working on glaucoma devices, Lee tackled other long-term implants, including a drainage device for hydrocephalus, a buildup of fluid in the brain.

Broadly, Lee’s lab focuses on improving the long-term implants available in clinics today. “Doctors and surgeons are already familiar with the form factors of these existing medical devices,” Lee said. “We're trying to add additional functionality using these microscale features.”

The tubes of ocular drainage devices need to last many years, so Lee sees self-cleaning functionality as an important priority. Surgically implanting extra drainage is no help if proteins, antibodies, or scar tissue render the piping useless.

As they began this project, Lee and his students envisioned installing tiny rectangular cantilevers into glaucoma drainage tubing. But the smaller scale of the project required a different approach.

To speed up design iteration, Lee and his team created the microfeatures from off-the-shelf materials, such as copper-clad liquid crystal polymer sheets and equipment typically used to manufacture semiconductor devices. They opted to shape the features using maskless photolithography, a more adaptable route than conventional wafer-based fabrication.

They decided on a lengthened cantilever beam with an arrow at the beam’s free end. To make the beams more flexible, they etched away several microns of material, then plated the beams with nickel to make them magnetic. Finally, they coated the entire feature in titanium to reduce the risk of irritation in the body.

The experiments focused on setting three beams in a line.

Having multiple devices opened up the possibility of more precision. Lee’s team is interested in using varied features — changing a beam’s thickness, or its nickel plating, to produce different vibrations — in different tubing sections for targeted cleaning.

Ultimately, each beam is still much smaller than its drainage tube housing, so dislodging a patient’s implant with these varied vibrations isn’t a problem.

From a clinical perspective, Dr. Andrew Iwach, an ophthalmologist and executive director of the Glaucoma Center of San Francisco, sees another avenue of use for these microfeatures.

In Iwach’s experience, scar tissue tends to cause many issues with glaucoma drainage implants. By controlling fluid flow, a drainage device souped-up with with microcantilevers could possibly discourage the growth of scar tissue.

“We actually may be able to leverage the flow in the tube to benefit the early phase of healing,” he said.

Still, a surgically implanted device is a more invasive option than the eye drops or laser treatments that can help patients in the initial stages of glaucoma. “We generally reserve glaucoma drainage devices for more severe cases,” Iwach said.

Patients with advanced glaucoma might rely on these implants for years, so improving their longevity could be a boon.

Next, Lee and his students are beginning animal testing. They’re downsizing these devices for experiments in mice.

To make many devices at once, they’ll transition their finalized prototype back to conventional fabrication methods.

As experiments progress, Lee and his students will work with larger animals to test the devices at scales more relevant to humans. Eventually, these tiny beams could help maintain plumbing within the human eye, allowing many patients to manage glaucoma longer than they have in the past.